utils/conv_gen.py: separate code definitions

This change separates the convolutional code definitions from the code
generator logic, allowing us to make further changes in more specific
way. For example, adding some new codes, you change the conv_codes.py
only because such change isn't related to the generator.

Change-Id: I3428561251b7d7a180d1e9b6fcaad50bdbbc37fa
2 files changed